1. Field of the Invention
This invention relates to an ion implanter, and more particularly to an ion implanting chamber of the ion implanter with a temperature monitor.
2. Description of Related Art
As the integration of an integrated circuit (IC) rises, precise IC fabrication becomes more essential. This is because any little error in IC fabrication may cause an IC fabrication failure. A subsequent undesired result of such failure is that a lot of wafers may be partially or fully damaged and therefore the fabrication cost increases.
Currently, ion implantation technology can provide a doping process in IC fabrication. Because doping distribution can be more precisely controlled by ion implantation technology than by a thermal diffusion technology,, especially with regard to the depth and dopant density profile, ion implantation becomes the main doping technology in very large scale integration (VLSI) fabrication for IC devices.
An ion implanter used for ion implantation is a complicated piece of equipment with a huge volume. The ion implanter is distinguished according to its potential dopant density, either as a high current type with about 10 mA of ion beam or a medium current type with about 1 mA of ion beam. An ion beam like a particle line is composed of a large number of ion particles in close proximity to each other and continuously travelling together so that dopant density is expressed in the current unit. Since the cross-sectional beam size is tiny, an ion beam scanner is needed to fully dope an entire semiconductor wafer with two-dimensional large regions.
The available ion beam scanners are basically divided into two categories: an electronic type of scan plates design and a mechanical type of spin disk design.
For the scan plates type scanner, the ion beam travels in between two pairs of parallel plates. The parallel plates produce an electric field transverse to the beam direction to deflect the ion beam so that the two pairs of parallel plates can two-dimensionally deflect the ion beam to the desired places to perform a scan on the fixed wafer. Theoretically, the scan plates type scanner makes use of deflection on the ion beam to dope the wafer in the desired region.
For the spin disk type scanner, the operation is on the contrary to the scan plates type. The ion beam direction is fixed but the wafer location is moving to get wafer doped. There are many wafers mounted on a spin disk plate. When doping is performed, the spin disk plate not only fast rotates but also moves following a special track so that the wafers on the spin disk pate can be uniformly doped.
Regardless of whether the machine is a scan plates scanner or a spin disk scanner, the doping is always performed in an ion implanting chamber. FIG. 1 is schematic for a conventional ion implanter chamber. The ion implanting chamber shown in FIG. 1 is used in an ion implanter with a spin disk scanner, for example, the E500HP.TM. or VIISION80.TM. provided by the VARIAN company. In FIG. 1, inside an ion implanting chamber 10, an ion beam 18 is produced by the ion implanter and shoots onto a number of wafers 14, which are mounted on a wafer mounting disk 12 in circular sequence. The wafer mounting disk 12 is mounted on a motor 16, which is cooled by a cooling system 20. The motor 16 can rotate the wafer mounting disk 12 and the wafer mounting disk 12 can be moved up and down so that the wafers 14 on the wafer mounting disk 12 can be uniformly doped. The ion implanting chamber 10 is also used for an ion implanter with the scan plates scanner, in which the ion beam 18 moves but the wafer-mounting plate 12 does not move.
When the ion beam 18 is doping the wafers 14, the ion energy of about 10-200 KeV causes the wafers 14 to rise in temperature. The high temperature can change the properties of a photoresist (not shown) formed on the wafers. As a result, for example, junction depth and dopant density are not controlled as desired, which causes a fabrication failure. In order to prevent the deterioration of the photoresist from ion implantation, the currently available ion implanter includes the cooling system 20 to cool the wafers 14. However, the cooling system 20 only indirectly cools the wafers 14 through the wafer mounting disk 12 so that the real temperature on the wafers 14 cannot be precisely monitored. In this case, a high rise in temperature on the wafers 14 would cause fabrication failure.
Currently, the temperature measurement is taken only at a testing stage, by tagging a temperature tag (not shown) on the surface of a control wafer, which is like the wafers 14 but for control test only. The temperature of the control wafer is obtained by observing the color change of the temperature tag. This kind of temperature measurement has the following several drawbacks:
1. It is only suitable for the control wafer because the temperature tag is never tagged on the wafers 14 in real fabrication. PA1 2. The temperature measurement process is not convenient because it is necessary to place the temperature tag and observe it by eye. PA1 3. The temperature of the wafers 14 in actual fabrication cannot be measured. PA1 4. The temperature measurement taken with the temperature tag is not sufficiently precise.